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Rapid Fire Abstracts

Rapid Fire 02- Tissue Characterization I

Left Atrial Fibrosis Quantification using an Accelerated 3D Left Atrium Late Gadolinium Enhancement Pulse Sequence with Isotropic Spatial Resolution: A Preliminary Evaluation in Patients with Atrial Fibrillation (RF_TH_210)

Thursday, January 30, 2025
2:20 PM – 2:30 PM East Coast USA Time
Location: Blue Room PreFunction
Background: While catheter ablation of atrial fibrillation (AF) is the most effective rhythm control, the recurrence of AF post ablation is 20-40% [1]. Despite the negative results of the DECAFF II trial, left atrial (LA) fibrosis measured by 3D late gadolinium enhancement (LGE) remains a widely accepted substrate for initiating and sustaining AF and plays a significant role in the AF begets AF mechanism [2]. The 3D LGE sequence used in the DECAFF trial had relatively poor spatial resolution (2.5 mm slick thickness) [3]. To our knowledge, no other group has published the application of a 3D LA LGE pulse sequence with high isotropic spatial resolution (1.5 mm3). We aimed to determine the clinical utility of a 3D LGE sequence with isotropic spatial resolution for quantifying LA fibrosis in AF patients compared with healthy controls.

Methods: Twelve AF patients scheduled for first-time ablation underwent CMR at 1.5 T (Siemens) between August 2023 and August 2024 in a multi-center study. During that same span, we enrolled 12 healthy control subjects. Subject demographics are summarized in Table 1. We modified a preciously described 3D LA LGE pulse sequence [4] using a stack-of-stars k-space sampling pattern and extra motion-state golden-angle radial sparse parallel (XD-GRASP) reconstruction [5] to employ gradient recalled echo (GRE) readouts instead, in order to produce more robust image quality (see Figure 1 for the sequence diagram, reconstruction pipeline, and relevant image parameters). 3D LGE was performed approximately 20-30 min following double dose [6] of gadobutrol (0.20 mmol/kg) administration [7]. Images were analyzed using ADAS 3D (Galgo). The LA model includes the left atrial appendage and up to 1 cm of each pulmonary vein, excluding the mitral valve region [8]. LA fibrotic burden is measured using the image intensity ratio (IIR) method [9] with an IIR cutoff of 1.2 to determine fibrosis [10]. Raw LGE images were visually assessed by one radiologist on a 5-point Likert scale (1: non-visible; 3: acceptable, 5: excellent) to evaluate the conspicuity of the LA wall, graded on visibility of artifact, noise, and LA wall detection. Appropriate statistical analyses (t-test) were performed, where a P value < .001 was considered significant.

Results: The mean scan time was 7.9 ± 1.6 min. Figure 2 shows a processed fibrosis map (left panel) and LGE images in three orthogonal planes (right panel) for representative AF and control groups. The median conspicuity score was 4 (IQR: 1.25) The LA fibrotic burden was significantly (P< 0.001) higher for the AF group (39.1 ± 15.6%) than the healthy control group (13.9 ± 3.7%).

Conclusion: This study demonstrates that our new 3D LA LGE sequence with isotropic spatial resolution produces clinically acceptable image quality for quantification of LA fibrosis. The resulting LA fibrotic burden was sensitive to discriminate between AF and control subjects. The control group was significantly younger than the AF group, which may affect the influence of comorbidities (e.g., diabetes, hypertension, history of stroke). A limitation of this study is that the sample size is small. A future study with a higher number of patients is warranted.